1. Field of the Invention
The present invention relates to an ink jet recording apparatus which performs recording by discharging ink from nozzles onto a recording medium.
2. Description of the Related Art
Conventionally, this type of ink jet recording apparatus performs recording by driving an electromechanical transducing element such as a piezoelectric element or an actuator such as an electrothermal transducing element, thereby varying the pressure inside a pressure chamber connected to a nozzle such that ink in the pressure chamber is discharged from the nozzle onto a recording medium.
In recent years, there has been a tendency toward an increased number of nozzles and higher nozzle density in ink jet recording apparatuses in order to achieve higher recording quality. In such ink jet recording apparatuses, either the driver IC is enlarged or a plurality of driver ICs is provided to correspond to the increased number of nozzles. When the driver IC is enlarged, an expensive IC must be used due to low yield and so on, which is disadvantageous in terms of cost. In response to this, Japanese Patent Application Laid-open No. H8-258292 (see FIGS. 6 and 9) enables high-speed recording output by driving a plurality of independent decoders independently.
However, the use of a plurality of decoders is problematic. Particularly in terms of cost reduction, when driver ICs installed with an amp circuit having no feedback control are used, differences may arise among the driver ICs in the ON resistance (resistance in a conductive state) of the amp circuits, and at the same time variation may exist in the output current, output waveform, and other output characteristics of the driver ICs. For example, when a single nozzle array is divided into two groups and driving is performed using one driver IC for each group, differences in the ink droplet speed and ink droplet volume between the groups during discharge lead to tonal variation, printing deviation, and so on between the groups, causing so-called banding, in which a band-form boundary is formed between the groups.
FIG. 8 is a schematic view illustrating the printing condition when an actuator is driven using two driver ICs having different output characteristics. For example, a nozzle array 83 of a head 81 comprises nozzles N1 to N12. The upper nozzles N1 to N6 are connected to a driver IC 80a, and the lower nozzles N7 to N12 are connected to a driver IC 80b. The two driver ICs 80a and 80b have different output characteristics, and according to these output characteristics, the driver IC 80a has a tendency toward small droplet volume and early discharge timing, whereas the driver IC 80b has a tendency toward large droplet volume and late discharge timing. When a recording medium moves relative to the head 81 in a direction shown by an arrow X in FIG. 8, the nozzle array N1 to N6, driven by the driver IC 80a, produces a printing condition in which the dot diameter is small, as shown by a dot array 82a, and the nozzle array N7 to N12, driven by the driver IC 80b, produces a printing condition in which the dot diameter is large and the dots are deviated from the dot array 82a in the opposite direction to the arrow X in FIG. 8, as shown by a dot array 82b. In other words, the upper half of the printing area is printed palely, whereas the lower half is printed deeply, and hence a difference in the halftones of the color occurs. Moreover, since the discharge timing of the two driver ICs is different, printing deviation also occurs. Note that each of the dot arrays 82a, 82b occupies a substantially identical area. These differences in printing condition between wide areas such as the upper half and lower half of the printing area lead to the occurrence in the printing area of the aforementioned banding phenomenon.
To avoid this phenomenon, the individual output characteristics of the driver ICs must be matched between themselves. Methods which may be considered for this purpose include:
(1) measuring the output characteristics of driver ICs one by one and combining those having close characteristics; and
(2) selecting driver ICs manufactured in adjacent sites on a wafer.
However, both of these methods are laborious and expensive, and therefore not practical.